I. Field of the Invention
The present invention relates to the control of a fuel pump for a direct injection gasoline internal combustion engine.
II. Description of Material Art
Direct injection internal combustion engines, i.e. engines in which the fuel injector injects the fuel directly into the combustion chamber, exhibit several advantages over the more conventional port-fuel injected internal combustion chambers. Most notably, direct injection engines enjoy increased fuel economy over other types of internal combustion engines. Direct injection internal combustion engines, however, do exhibit some inherent disadvantages.
One disadvantage of the previously known direct injection internal combustion engines is that such engines exhibit excessive noise, which is particularly evident at low engine speeds. Such noise is attributable to noise from the fuel system.
A primary source of noise, especially at low speeds, for a direct injection engine arises from the fuel pump for the engine. Typically, a pump piston in a fuel pump is reciprocally driven by a cam having two or more typically three or four lobes. These lobes are all symmetrical and all contact the piston pump, usually through a roller. Upon rotation of the cam, the lobes cause the piston to move reciprocally within the pump housing.
The fuel pump also includes an inlet valve which is movable between an open position and a closed position by an electric coil or solenoid. In its open position, fuel flows to or from a pump chamber within the pump housing through the valve port. Conversely, when the valve is moved to its closed position, the piston during a pump cycle pumps pressurized fuel through a check valve and into the fuel rail for the engine.
The operation of the fuel pumps, however, causes significant noise, especially at low speeds, such as idle. A primary source of this noise is caused by the opening and closing of the valve.
More specifically, when the valve is moved to its open position by the electric coil or solenoid, the valve contacts a valve stop and produces an audible tick. Conversely, whenever the valve slams to a closed position during a pumping or pressurization portion of the pumping cycle, the contact between the valve head and the valve seat also causes audible noise. This noise is particularly prevalent at low speeds.
The rapid closure of the fuel valve is required for proper engine operation at high speed operation of the engine since the fuel pump operates at or near 100% of its capacity. However, such rapid closure of the fuel valve is not required at lower speeds, such as idle, due to the lower fuel requirements of the engine.